1. Field of the Invention
The present invention is a light emitting device, and more particularly is to form a plurality of pillar structure with hollow structure therein to increase the light extraction efficiency of the light emitting device.
2. Description of the Prior Art
The major reason for the lower output of illumination efficiency of the optical device, such as light emitting device, is the light extraction efficiency of the light extraction which is insufficient. That is to say, the actual illumination is emitted from the light emitting device that is part of the illumination of the active layer. Thus, a photon element is utilized in the light emitting device to improve the light extraction efficiency of the light emitting device in the conventional technology.
In the past, as shown in FIG. 1A, the semiconductor light emitting device with blue light includes a sapphire substrate 100; a GaN buffer layer 102 is disposed on the sapphire substrate 100; a n-type GaN semiconductor layer 104 is formed on the GaN buffer layer 102. Because the band gap of the active layer 106 is smaller than the band gap of the n-type GaN semiconductor layer 104, thus, the material of the active layer 106 can be InGaN compound semiconductor layer. The n-type semiconductor layer 104, the active layer 106, and p-type semiconductor layer 108 can be stacked to server as a semiconductor stacked layer. Next, a transparent conductive layer 110 is formed on the P-type semiconductor layer 108, and a p-side electrode 114 is disposed on the surface of the transparent conductive layer 110, and the n-side electrode 116 is disposed on the exposed surface of the n-type GaN semiconductor layer 104. In order to increase the closed efficiency for the carrier, the AlGaN with large band-gap can be used for the material of n-type GaN semiconductor layer 104 and P-type semiconductor layer 108 on the active layer 106.
In order to form the n-side electrode 116, the portion of semiconductor layer 108 is removed to expose the portion surface of the n-type semiconductor layer 104, and the width W is also formed by removing a portion of peripheral of light emitting device. Due to the hardness of the material of GaN semiconductor layer on the peripheral of the light emitting device is difficult to saw or carve, the formation of the active layer 106 is formed by dry etching process to avoid the crack is generated within the active layer 106. Further, the reflective index (reflective index is 2.5) of the GaN semiconductor layer is equally to the other compound semiconductor layer, and the reflective index is larger than the air (the reflective index is 1.0), and thus, the light is emitted from the active layer 106 through the semiconductor layer 108 to the air (not shown) that would be induced the total reflection, so as to the light would not emitted from the semiconductor layer 108 to the outside. Thus, the light is reflected repeatedly to increase within the semiconductor layer to decay of the illumination, so that the light extraction efficiency is decreased to 10%. In order to solve the light extraction efficiency of the light emitting device, as shown in FIG. 1B, in the GaP, AlGaInP, AlGaAs compound semiconductor layer, the concave and raised structure is formed around the peripheral of the light emitting device, so that the light can be extracted from the semiconductor stacked layer to the outside. As shown in FIG. 1B, the n-type GaP layer 202 and p-GaP layer 204 is formed as the semiconductor stacked layer, and p-side electrode 206 is disposed on the surface of the semiconductor stacked layer, and n-side electrode 210. After die sawing process, a plurality of LED die can be obtained, and an etching process such as hydrochloric acid (HCl) solution to form the rough surface among the concave and raised structure of the surface of the LED die.
In order to increase the light emitting efficiency, the current is applied to the electrode to increase the current density, but the reliability and usage life of the light emitting device would be decreased.